A-M/AGC Weighted Pre-Detection Diversity Combining

Abstract

A method has been proposed for improving the performance of automatic gain control (agc) weighted diversity combiners in the presence of fast fading radiofrequency (rf) signals by use of the amplitude modulation (a-m)(detected linear intermediate-frequency (i-f) envelope) in addition to the agc voltage to weight the combiner. Also suggested was a method for selecting the channel with the best signal-tonoise ratio (SNR) by use of the a-m and agc voltages. Experimental hardware has been constructed for evaluation of three configurations: an a-m/agc weighted combiner; an a-m/agc based selector; and an a-m/agc combiner/selector where the criterion for combine or select is determined by the phase error between the two channels. An experimental study was also conducted of the phase-locked loop (PLL) to determine the best configuration and parameter values for the combiner application (where relatively large phase errors are permissible). Data were taken under laboratory and operational (Vandenberg Air Force Base) conditions and are compared with data taken with a commercial agc weighted combiner.